In surgery, surgical observation systems have been proposed in which three-dimensional images are obtained from optical images of a surgical site with an image-acquisition optical system disposed at a desired position above the surgical site in a patient, and the obtained three-dimensional images are supplied to a lead surgeon (hereinafter simply referred to as “surgeon”) and an assistant, who is an assistant surgeon (hereinafter simply referred to as “assistant”), via monitors. In particular, in neurosurgery, because the surgeon and the assistant are located so as to form an angle of 90° with respect to the patient, the observation directions from the surgeon and the assistant to the surgical site differ by 90°. Therefore, with the surgical observation system, the surgeon and the assistant are respectively provided with three-dimensional images of the surgical site as viewed from the direction of each person (see Patent Literature 1).
Since the surgeon and the assistant perform the operation on the patient while observing the three-dimensional images of the surgical site displayed on the monitors, the housing that accommodates the image-acquisition optical system must be as compact as possible so as not to hinder the surgical procedure or viewing of the monitors by the surgeon and assistant during the surgery.
In the case where the observation directions of the surgeon and the assistant differ, as described above, to provide three-dimensional images as viewed from the direction of each person, it is necessary to obtain three-dimensional images of the surgical site from two different directions. Thus, in the surgical observation system, two image-acquisition optical systems having a pair of apertures disposed side-by-side are made to intersect each other, and two image-acquisition optical systems formed of a total of four apertures must be accommodated in the housing, which makes the housing large. A large housing hinders the surgical procedure or viewing of the monitors by the surgeon and the assistant during surgery.